1. Field of the Invention
The present invention relates to a tandem-type brake booster for assisting a brake in braking operation.
2. Description of the Prior Art
Brake boosters are required to assist the brake of an automobile in producing sufficiently large braking forces and to improve the "feeling" which the driver has on braking the automobile. To meet such requirements, attempts have heretofore been made to increase the volume of a closed shell or casing of the brake boosters. One effort has been directed to increasing of the diameter of the closed shell. According to another improvement, as schematically shown in FIG. 2(b) of the accompanying drawings, a closed shell or casing 10b is divided into front and rear chambers R, R having the same outside diameter, and power piston 20b, 30b are disposed respectively in the front and rear chambers R, R to provide a tandem construction having a pair of axially arranged constant- and variable-pressure chambers. The former proposal is disadvantageous in that the brake booster is radially increased in dimension. With the latter arrangement, the brake booster has an increased axial length. These prior brake booster constructions therefore fail to meet a present demand for smaller-size brake boosters.